The optical measurement of electrical currents using the Faraday effect has significant advantages, such as a high linearity of the response even for large currents, which is of importance for measurements under short-circuit conditions.
In order to measure the sum of two or more current with an optical sensor (such as described e.g. in EP 1 174 719), independent sensors each with its own control electronics can be used. The control electronics convert the physical measurements from the sensor to a digitized number. The numbers are then added to obtain the sum of the currents.